I was using Ember 1.5.0 in my project and now after almost 1 year I want to upgrade to 1.11.1.

All the templates were written in handlebars.

Now I’m using ember 1.11.1 debug and also ember-template-compiler.js, but it’s throwing error while compiling templates.
(I just changed the library and didn’t do any modification in my code, cause 1.11.1 has backward compatibility and by the warnings thrown in the console I wanna find out where I should modify the code)

HTMLBars uses Handlebars syntax, you should not need to rewrite any of your templates to update to Ember 1.10/1.11.

You will, however, need to update your template precompilation process. The work involved here is dependent on what you are using today for this task. To give an idea of the process I wrote up a blog post on how to precompile templates in 1.10+ here.